Various kinds of the tuning amplifiers using active elements and reactance elements have been conventionally proposed and put to practical use.
For example, the tuning amplifier of the prior art utilizing LC resonance is characterized in that when the tuning frequency is adjusted, Q and a gain depending on a LC circuit are varied, and when the maximum attenuation is adjusted, the tuning frequency is varied, and when the maximum attenuation is adjusted, the gain in the tuning frequency is varied. Consequently, in the tuning amplifier of the prior art, it was extremely difficult to adjust the tuning frequency, the gain in the tuning frequency and the maximum attenuation of C1, C2 without interference to each other. Also, it was difficult to form the tuning amplifier capable of adjusting the tuning frequency and the maximum attenuation by an integrated circuit.